QTL viewer description. This is a diagrammatic view describing the inputs and outputs from the database and viewer. QTL and marker information are assembled from the literature or web sites and entered into the linked, discrete marker and QTL databases. The integrated marker/QTL database serves as the back end for queries emanating from the user interface (viewer). The viewer will display different views depending on user choices which can ultimately be resolved to single QTL details with links to literature and markers.